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Carles Triguero

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  1. Title: Origin of scale-free intermittency in structural first-order phase transitions

    Author(s): Perez-Reche F.J., Triguero C., Zanzotto G., Truskinovsky L.

    Physical Review B, 94, No. 14, pp. 144102- (1 October 2016)

    doi: 10.1103/PhysRevB.94.144102
    Abstract


    Full Text

    A salient feature of cyclically driven first-order phase transformations in crystals is their scale-free avalanche dynamics. This behavior has been linked to the presence of a classical critical point but the mechanism leading to criticality without extrinsic tuning remains unexplained. Here we show that the source of scaling in such systems is an annealed disorder associated with transformation-induced slip which coevolves with the phase transformation, thus ensuring the crossing of a critical manifold. Our conclusions are based on a model where annealed disorder emerges in the form of a random field induced by the phase transition. Such a disorder exhibits supertransient chaotic behavior under thermal loading, obeys a heavy-tailed distribution, and exhibits long-range spatial correlations. We show that the universality class is affected by the long-range character of elastic interactions. In contrast, it is not influenced by the heavy-tailed distribution and spatial correlations of disorder.

  2. Title: Understanding Adsorption-Induced Structural Transitions in Metal-Organic Frameworks: From the Unit Cell to the Crystal

    Author(s): Triguero C., Coudert F., Boutin A., Fuchs A.H., Neimark A.V.

    The Journal of Chemical Physics, 137, No. 18, pp. 184702- (14 November 2012)

    doi: 10.1063/1.4765369
    Abstract



    Breathing transitions represent recently discovered adsorption-induced structural transformations between large-pore and narrow-pore conformations in bi-stable metal-organic frameworks such as MIL-53. We present a multiscale physical mechanism of the dynamics of breathing transitions. We show that due to interplay between host framework elasticity and guest molecule adsorption, these transformations on the crystal level occur via layer-by-layer shear. We construct a simple Hamiltonian that describes the physics of host-host and host-guest interactions on the level of unit cells and reduces to one effective dimension due to the long-range elastic cell-cell interactions. We then use this Hamiltonian in Monte Carlo simulations of adsorption-desorption cycles to study how the behavior of unit cells is linked to the transition mechanism at the crystal level through three key physical parameters: the transition energy barrier, the cell-cell elastic coupling, and the system size.

  3. Title: Structural Transitions in MIL-53 (Cr): View from Outside and Inside

    Author(s): Neimark A.V., Coudert F., Triguero C., Boutin A., Fuchs A.H., Beurroies I., Renaud Denoyel R.

    Langmuir, 27, No. 8, pp. 4734-4741 (18 March 2011)

    doi: 10.1021/la200094x
    Abstract



    We present a unified thermodynamic description of the breathing transitions between large pore (lp) and narrow pore (np) phases of MIL-53 (Cr) observed during the adsorption of guest molecules and the mechanical compression in the process of mercury porosimetry. By revisiting recent experimental data on mercury intrusion and in situ XRD during CO2 adsorption, we demonstrate that the magnitude of the adsorption stress exerted inside the pores by guest molecules, which is required for inducing the breathing transition, corresponds to the magnitude of the external pressure applied from the outside that causes the respective transformation between lp and np phases. We show that, when a stimulus is applied to breathing MOFs of MIL-53 type, these materials exhibit small reversible elastic deformations of lp and np phases of the order of 2−4%, while the breathing transition is associated with irreversible plastic deformation that leads to up to ∼40% change of the sample volume and a pronounced hysteresis. These results shed light on the specifics of the structural transformations in MIL-53 (Cr) and other soft porous crystals (SPC).

  4. Title: Mechanism of Breathing Transitions in Metal–Organic Frameworks

    Author(s): Triguero C., Coudert F., Boutin A., Fuchs A.H., Neimark A.V.

    Journal of Physical Chemistry Letters, 2, No. 16, pp. 2033-2037 (22 July 2011)

    doi: 10.1021/jz2008769
    Abstract



    We present a multiscale physical mechanism and a stochastic model of breathing transitions, which represent adsorption-induced structural transformations between large-pore and narrow-pore conformations in bistable metal–organic frameworks, such as MIL-53. We show that due to interplay between host framework elasticity and guest molecule adsorption, these transformations on the level of the crystal occur via layer-by-layer shear. We construct a simple Hamiltonian that describes the physics of host–host and host–guest interactions and show that a respective Monte Carlo simulation model qualitatively reproduces the experimentally observed features of breathing transitions.

  5. Title: Magnetocaloric effect in metamagnetic systems

    Author(s): Triguero C., Porta M., Planes A.

    Physical Review B, 76, No. 9, pp. 094415- (24 September 2007)

    doi: 10.1103/PhysRevB.76.094415
    Abstract



    We propose a model to account for the magnetocaloric effect associated with field-driven first-order magnetic transitions. The model is based on an Ising model for the magnetic degrees of freedom which are coupled to lattice vibrations. The coupling is introduced within the framework of a bond proportion model, which assumes that nearest-neighbor pairs of antiparallel and parallel spins have different stiffness. The model is solved by means of a variational mean field technique and it is found that, for strong enough coupling, it displays a field-induced first-order magnetic transition. The magnetocaloric properties are obtained and results are compared with experimental results reported for systems undergoing metamagnetic transitions.

  6. Title: Coupling between lattice vibrations and magnetism in Ising-like systems

    Author(s): Triguero C., Porta M., Planes A.

    Physical Review B, 73, No. 5, pp. 054401- (1 February 2006)

    doi: 10.1103/PhysRevB.73.054401
    Abstract



    In this paper the bond proportion model is introduced as a prototype of a system with coupled magnetic and vibrational degrees of freedom. This model is generalized within the framework of cluster expansions in order to achieve invariance of the potential energy to a rotation of the crystal. First, the original bond proportion model is solved in the mean-field approximation and by means of numerical simulations. It has been found that the temperature and the smoothness of the magnetic phase transition depend on the strength of the magnetoelastic coupling. For a large enough entropy difference between the magnetic phases the phase transition becomes first order. This is evidenced by means of the computation of the magnetization, the elastic constants, and the total entropy. The numerical simulation of the modified bond proportion model has revealed significant differences with respect to the bond proportion model in the heat capacity around the phase transition and, consequently, in the entropy difference between the magnetic phases. Small differences in the elastic constants are also detected.